Stump diameter and age affect coppicing of downy birch (Betula pubescens Ehrh.)

Abstract

Downy birch is a primary successional tree species colonizing open areas and thriving on peatlands. Short-rotation coppice management in natural, dense, downy birch stands could be one management option. The effect of stump diameter, stump height and stand age on the sprouting of downy birch was studied by clear-cutting six stands from three age classes (A: 10–12 years, B: 15–16 years, C: 22–24 years) located in northern Finland and measuring the sprouts in the following autumn. The percentage of non-sprouting stumps increased with the stand age (A: 9%, B: 14%, C: 27%). The smallest (< 1 cm) and biggest (> 9 cm) stumps showed higher mortality than medium-sized stumps. Sprouts originated close to the ground level: over 50% were located below 2 cm from the ground level. An increase in the diameter of stumps led to higher numbers of sprouts produced per stump, and higher mean, dominant and cumulative height of sprouts per stump and higher biomass of sprouts per stump. The effect of the diameter on the growth of sprouts depended on the stand age. In the same diameter class, the mean height, dominant height and biomass per stump were higher the younger the stand was. The biomass per stump correlated best with the total height of the sprouts on a stump. The results have implications for strategies in controlling sprouting in coniferous stands and for stand management practices when the aim is to grow downy birch coppices.